The present invention is directed to an acrylic polymer emulsion, which, when blended with an elastomeric material can be used as a coating for use on various products. One especially useful application is for coating a film or paper substrate for use as a sheet upon which images may be printed with ink jet printers. When applied to paper or film to produce print sheets, the coating provides a high quality, clear, glossy surface that freely receives water based inks such as are commonly used with ink jet printers. These properties make print sheets coated with the polymer especially useful as photographic quality papers and transparencies for use with ink jet printers. Another application for the polymer is for coating rubber articles such as gloves. When applied to such rubber articles, excellent mold release, donning and anti-blocking properties can be achieved.
Ink jet printing is a well-known and commonly used means of producing an image onto a substrate. Ink jet printers typically use one of two different types of ink, dye-based inks and pigment-based inks. With dye-based ink, the color of the ink is imparted by a dye that is soluble in a fluid carrier. The fluid carrier is typically a blend of water and glycol. Such dye-based inks are relatively inexpensive and easy to process, and are suitable for use in low cost applications in which long term durability is not a concern. In pigment-based inks, the color is imparted by particles that are dispersed, rather than dissolved, in a fluid carrier. Water-soluble fluids are typically used as the carrier for pigment-based ink for improved lightfastness.
Some of the most recent advances in ink jet printer technology have been in the area of photo-quality or near photo-quality printing. While printers and inks are able to achieve the high resolution necessary for photo-quality printing, many of the printing papers and other printing films (such papers and films collectively referred to in this specification as xe2x80x9cfacestocksxe2x80x9d) available to the consumer fail to permit the consumer to take full advantage of the printer""s capabilities. A first shortcoming is that many of the photo-quality facestocks that are capable of high-resolution photo-quality printing do not impart sufficient glossiness to match that of prints made on photographic paper by traditional photographic techniques. A second shortcoming is that many of the photo-quality facestocks with the desired glossiness are incapable of the high resolution desired for a photo-quality print. To the extent that some facestocks have been able to achieve both high gloss and high resolution, still further problems such as slow dry times are often realized. It is important that the ink applied to a facestock be able to dry fast to permit the handling of the print soon after printing, and to allow printed sheets to be stacked in a printer""s output tray without resulting in any smearing the printed images.
In order to meet the print facestock requirements for high gloss, good ink absorbency and fast print drying, prior art ink jet facestock technology often relies on the use of various coatings which are applied to a substrate. For many such coatings, multiple layers are required which tend to require elaborate, and therefore, expensive manufacturing techniques. Many coatings also require mechanical treatment such as the use of a polished casting drum in order to achieve the desired glossiness, a step that still further adds to the manufacturing cost. Moreover, such facestocks still tend to be slow drying, making them susceptible to smearing of the printed images. Improved facestock coatings that are fast drying, glossy and capable of high-resolution are desired for the production of facestocks used for photo-quality computer printing applications.
Rubber articles made from natural or synthetic rubber include surgical gloves, physician examining gloves, industrial work gloves, prophylactics, catheters, balloons, tubing, sheeting and the like. Some of these articles, and in particular gloves, require good donning properties, that is, the ability of the rubber article to be slid on and off skin surfaces without undue clinging or friction. Surgical gloves require good wet donning properties, that is, the ability to be slid over damp or wet skin surfaces. Physician examining gloves and industrial work gloves require good dry donning properties, that is, the ability to be slid over dry skin surfaces.
The comfort of such a glove, whether worn for surgical use, examination use, or industrial use, can generally be improved, especially if the glove is worn for a prolonged period of time, if the inside of the glove is absorbent. Furthermore, good absorbency properties in which the buildup of moisture within a glove is prevented can improve the wearer""s dexterity. However, while absorbency is desirable, the absorbency of a rubber article such as a rubber glove cannot be permitted to compromise the barrier properties required of such gloves.
Another desirable property for gloves and other rubber articles is that the outer surfaces permit such articles to be stacked against one another without sticking or xe2x80x9cblockingxe2x80x9d to one another. Of course, neither should the interior of a glove or other rubber article stick to itself as such blocking makes donning difficult.
It is also desirable that any coating that is to be applied to the mold side of the article impart good mold release properties. Without good mold release properties, the finished articles can be difficult to remove from the molds, especially if mechanical devices are used for stripping the finished articles from the molds. Without good mold release properties, a significant number of articles may be torn during the stripping step. Yet another benefit of a coating with good mold release properties is that it simplifies the cleaning of the mold. This is important, as a single mold should be capable of producing a large number of articles without having to be taken off the manufacturing line for elaborate cleaning procedures.
To achieve the desirable characteristics for gloves and other rubber articles, various coatings have been developed. Such coatings can be applied to the inner, outer, or both surfaces of the rubber article. One of the simplest coatings has been to apply a powder such as talc or cornstarch to the surfaces of the article. The use of such a powder improves both the donning and blocking characteristics of such gloves.
The conventional way of manufacturing rubber articles such as powdered gloves has been to dip a mold or former, having the shape of the article to be formed, into a coagulant slurry containing both powder and a coagulant such as calcium nitrate or calcium carbonate. After drying, the mold is immersed in a rubber emulsion for a time sufficient for the rubber to coagulate and form a coating of desired thickness. Water leaching is generally employed as the next step in order to remove rubber impurities. Once the leaching process has been completed, the rubber article is then cured and dipped into a starch slurry. The starch-coated surface is then dried, leaving a coating of powder on the surface of the glove. After cooling, the rubber article is stripped from the mold. For most rubber articles, the stripping step results in the glove being turned inside out. The mold is then cleaned and used again for making another article.
An important drawback to the use of powder-coated gloves and other articles is that for many applications, the powder can contaminate the environment in which the wearer of the article is working. For example, for certain surgical procedures, powder-coated gloves are unacceptable as such a powder coating can contaminate the surgical field. Similarly, for gloves worn in clean rooms such as are commonly found in the electronics industry, the powder coating of a rubber glove can cause undesirable contamination of the clean room. Therefore, coatings are desired which can achieve the desirable donning and blocking properties for rubber articles without the use of powders.
Methods and materials used for glove manufacture are described, for instance, in U.S. Pat. Nos. 3,411,982 and 3,286,011 to Kavalier et al., both incorporated herein by reference, xe2x80x9cPolyurethane Latexes for Coagulation Dipping,xe2x80x9d Sadowski et al., Elastomerics, August 1979, pp. 17-20, incorporated herein by reference, and xe2x80x9cDipping with Natural Rubber Latex,xe2x80x9d Pendler et al., Natural Rubber Technical Bulletin, 1980, also incorporated herein by reference.
One way to eliminate the traditional powder coatings for gloves has been through the use of one of various surface treatment methods for the finished article. One such surface treatment method requires the halogenation of the surface of the article. Chlorination is the most commonly used of such methods. However, while effective, such treatments are often expensive. Moreover, they often have adverse affects on the shelf life of the rubber articles formed. It would be desirable to provide a rubber article with a powder-free donning surface without resorting to the expensive and article-deteriorating practices that are now commonly used. Such a process could substantially reduce the cost of manufacture and maximize the shelf life of the rubber article.
Other methods of making powder-free rubber articles such as gloves have included the use of coatings with silicon-based chemicals. However for the clean rooms employed in electronic chip manufacturing activities, the inclusion of silicon in the coatings is unacceptable as it can cause silicon contamination of delicate electronic components. Therefore, a coating for gloves and other rubber articles that is both powder-free and silicon-free while providing good donning, mold release and anti-blocking properties is desired.
The present invention sets forth a polymer emulsion useful for forming a coating a number of different products. The polymer emulsion is produced as the reaction product of a monomer mixture comprising an alkyl (meth)acrylate, a quaternary amine (meth)acrylate, a hydroxyalkyl (meth)acrylate, an N-vinyl lactam, an ethylenically unsaturated carboxylic acid, and a fluorinated (meth)acrylate. Additionally, a hard monomer and/or an ethoxylated (meth)acrylate monomer may be provided. The polymer emulsion is produced under vigorous mixing and preferably in the presence of a plurality of surfactants to further ensure good mixing. In the preferred embodiment, the polymer emulsion is made by a sequential polymerization reaction of two different monomer mixtures. For such a sequential polymerization reaction, the first monomer mixture is first allowed to partially react before the second monomer mixture is added to the reactor. Improved properties for the resulting polymer coating result when the second monomer mixture has a lower amount of ethylenically unsaturated carboxylic acid than the first monomer mixture. In particular, when such a sequential polymerization reaction is used, the resulting polymer emulsion has a lower viscosity at higher solids concentration than would otherwise be achieved if a single monomer mixture were reacted. By having a lower viscosity at a higher solids content, the polymer emulsion is far easier to handle.
The polymer emulsions of the present invention are useful in forming coatings for a variety of materials. As one example, the coatings can be applied to a facestock such as paper or vinyl in order to make a coated facestock for use in ink jet printing applications. Such coated facestocks exhibit excellent clarity and gloss characteristics, are fast drying and permit the printing of high-resolution photo-quality images using ink jet printers. Furthermore, even though such coated facestocks exhibit high gloss, they are still highly flexible and resist cracking and separation from the substrate. Moreover, the coated facestocks are easily fed through ink jet printers without causing jamming or other difficulties for the printer. Preferably, the coating is formed by diluting the polymer emulsion with an elastomeric material such as a nitrile rubber latex to a concentration of about 95% polymer emulsion. The coating is applied to a facestock at a dry coat weight of between about 10 and about 50 grams per square meter.
The polymer emulsions are additionally useful in forming coatings for rubber articles. For molded rubber articles, such coatings exhibit excellent mold release properties, even when mixed with a high concentration of coagulants such as calcium nitrate which are often used in the forming of nitrile rubber latex articles. In addition to outstanding mold release properties, the coatings provide excellent anti-blocking properties when applied to the outside surface of the rubber article. When applied to the inside surface of a rubber article such as a rubber glove, the coatings still further provide excellent donning properties, for both wet donning and dry donning applications. Moreover, the absorbency imparted to an article such as a glove whose inside surface is coated with the polymer coating of the present invention make the glove more comfortable to wear for extended periods of time. Preferably, such a polymer coating is formed by diluting the polymer emulsion with an elastomeric material such as a nitrile rubber latex. Preferably, the polymer emulsion is diluted with nitrile rubber latex to a concentration of about 25% by weight on a dry basis. The resulting emulsion of polymer and nitrile rubber latex is then diluted with water to a concentration of between about 2 and 8% solids to form a coating for a nitrile rubber article. Articles coated with the polymer coating of the present invention are strong, flexible and exhibit very high stretch without appreciable cracking or separation of the coating from the article. Such coatings can be applied to natural latex articles as well as to nitrile rubber latex articles.